270 STATE BOARD OE} AGRICULTURE. 



In the case of carbon dioxide immediately after milking, six analyses give in 

 percentages 



59.31, 55.33, 58.27, 6G.1, 65.65 and 53.28. 



The average of these is 59.63% per cent. 



The oxygen content has also undergone a marked change by the process of milking 

 as compared with non-exposure to the air. We obtained as the oxygen content of 

 milk in six analyses, 



2.88, 3.09, 2.69 ? 2.14, 1.6 and 2.12 per cent. 



The average of these is 2.42 per cent. 



After the milk had been exposed to the air by the process of milking there was 

 obtained, 



13.79, 12.66, 14.17, 11.89, 10.96 and 15.57. 



The average of these is 13.17% per cent. There has therefore been an increase in 

 the oxygen content of milk after milking over the oxygen content of unexposed milk 

 of 10.75% per cent. Further the percentages of residual gas drawn from the udder 

 without exposure to the air is 



16.54, 18.56, 18.27, 15.89, 18.24 and 11.71. 

 The average of these is 16.53% per cent. After the milking process the percentages 

 of residual gas are in six analyses, 



26.9, 32.01, 27.56, 22.01, 23.39 and 31.15. 



The average of these is 27.17 per cent, a gain of 10.63%, per cent in the residual gas 

 over the residual gas in unexposed milk. There was a gain of oxygen and residual gas 

 of 10.75% per cent and 10.63% per cent respectively, or in all 21.39% per cent. There 

 was a loss of 21.84 per cent in the case of carbon dioxide. Therefore, we find that 

 these averages practically offset each other. 



The percentages of oxygen to total gas less carbon dioxide in milk unexposed to the 

 air were in six analyses 



10.29, 14.09, 14.70, 11.86, 8.06 and 15.26 per cent. 



After milking the percentages of oxygen to total gas less carbon dioxide are in six 

 analyses 



33.83, 28.19, 33.88, 25.16, 32.16 and 31.96 per cent. 



From an examination of these two sets of results assuming that we are considering 

 the relation of oxygen to nitrogen as they exist in the air it will at once be noticed 

 that there has been a decided interchange in the relationship of oxygen to total gas 

 less carbon dioxide due to change of gases between the air and milk during the process 

 of milking; further, these two sets indicate that there is a chemical change going on 

 rather than a mere mixing of air and milk, because we should expect that were it a 

 mere solubility of oxygen and residual gas (perhaps nitrogen) the relationship would 

 be as 33.9 to 66.1 as has been stated. 



VI. ANALYSES OF GAS-CONTENT OF MILK DIRECTLY AFTER AERATING OVER GLASS. 



To understand what is effected by aeration a study of the gas-content of milk was 

 made after it had been subjected to a specially devised process of aeration. The common 

 methods of aeration were not employed on account of our inability to cope with the 

 necessary requirements of such experiments with the facilities at hand. It would be 

 absolutely essential that in such methods, a milk should be used under our control 

 from the time it leaves the udder, and the aeration should also have to be under our 

 direct supervision. Since such methods were ruled out from necessity, we resorted to 

 methods which would simulate the methods in vogue as closely 'as possible. 



A piece of glass six feet long by two inches wide was placed on an inclined board at 

 an angle of about twenty degrees. Over this the milk was run drop by drop, making 

 a film approximately of the extent of surface as indicated in the table. The amount of 

 milk aerated during the process is also given. Room temperature varying from 18 5 

 to 20° C. was employed during aeration and was found to be the only temperature 

 which could be satisfactorily used unless a special plant for aerating were constructed. 

 The analyses of gases obtained from milk aerated over glass were conducted the same 

 fts with milk after milking. 



